Trig. substitution

Greetings,

How is the integral (file attached) solved?

Correction: the integrand should be squared, as it equals x^2

I am aware of the pythagorian identities (cos^2x + sin^2x = 1, thus cos^2x = 1 - sin^2x). I have solved an integral with just a dx in the numerator but I have never solved an integral with an x^2 in the numerator. I don't what to do with it.